The synthesis and reactivity of alpha,beta-unsaturated thioamide, thioester, and thione iron tricarbonyl complexes.

Abstract

$\alpha,\beta$-Unsaturated thioamide, thioester and thione iron tricarbonyl complexes 1-13 were prepared from the free ligands and iron pentacarbonyl using photolysis or diiron nonacarbonyl using thermolysis. X-ray crystal structures were obtained for the free ligand 2$\sp\prime,$ (PhCH=C(Ph)C(S)NEt$\sb2$), and for complexes 1 and 2, $\rm\lbrack \overline{\overline{Fe(PhCH}{=}CHC(S})NEt\sb2)$(CO)$\sb3\rbrack$ and $\rm\lbrack \overline{\overline{Fe(PhCH}{=}C(Ph)C(S})NEt\sb2)$(CO)$\sb3\rbrack$ respectively. Thioamide and thioester iron tricarbonyl complexes gave triphenylphosphine substituted complexes 17-19 resulting from loss of a carbon monoxide ligand by photolysis or thermolysis. It was not possible to substitute more than one triphenylphosphine into the complexes. Thioamide and thioester ligands could be removed from the iron tricarbonyl fragment using ceric ammonium nitrate, hydrogen peroxide, m-chloroperbenzoic acid, or thermolysis. The best results were obtained with ceric ammonium nitrate, which minimized conversion of the C=S functional group to C=O. Thioester complex 10, $\rm\lbrack \overline{\overline{Fe(PhCH}{=}CHC(S})OEt)(CO)\sb3\rbrack,$ reacted with hydrogen peroxide or m-chloroperbenzoic acid to give the sulphine complex 20, $\rm\lbrack \overline{\overline{Fe(PhCH}{=}CHC(S}{=}O)OEt)(CO)\sb3\rbrack.$ Nucleophiles reacted with thioamide and thioester iron tricarbonyl complexes at room temperature affording 1,4-Michael addition products free of metal coordination. At $-$78$\sp\circ$C, nucleophiles reacted with thioamide iron tricarbonyl complexes forming 4-oxo-thioamide non-metal coordinated products. An electrophile reacted with thioester tricarbonyl complex 10 to give an S-alkylated cationic complex 21, $\rm\lbrack\lbrack\overline{\overline{Fe(PhCH}{=}CHC(S} {\sp+}$-Me)OEt)(CO)$\sb3 \rm\rbrack \lbrack BF\sb4\sp-\rbrack\rbrack.$ Alkynes added to the metal-coordinated olefin of $\alpha,\beta$-unsaturated thioamide iron tricarbonyl complexes 1, 4, $\rm\lbrack\overline{\overline{Fe(MeCH}{=}CHC(S})NEt\sb2)$(CO)$\sb3\rbrack,$ and 7, $\rm\lbrack\overline{\overline{Fe(MeCH}{=}CHC(S})N(Ph)$(Me))(CO)$\sb3\rbrack,$ generating complexes 22-26 possessing a cyclopentenone ligand. An X-ray crystal structure was obtained for complex 22. Silicon alkoxides were used as a source of alkoxide to prepare carboxylic esters in good yields from benzylic bromides and carbon monoxide catalyzed by a rhodium (I) complex under mild conditions.